1. Technical Field
Embodiments of the invention relate generally to power converters. Other embodiments relate to a switch apparatus for power converters.
2. Discussion of Art
In the rail industry, rail vehicles are utilized to transport passengers and/or cargo from location to location on a track. Typically, a locomotive provides the tractive power for a train. The locomotive is connected to pull or push the remainder of the train, and has traction wheels engaged with the track. In modern designs, the traction wheels are driven by electric wheel motors, which are powered via electrical distribution from one or more engine-driven generators housed within the locomotive. The traction wheels and wheel motors can be reversibly configured, to also act as brakes for slowing the locomotive.
Similarly, in the mining industry, large off-highway vehicles (“OHVs”) usually employ electrically motorized wheels for propelling or retarding the vehicle. In particular, OHVs typically use a large horsepower diesel engine in conjunction with an alternator, a main traction inverter, and a pair of wheel drive assemblies housed within the rear tires of the vehicle. The diesel engine is directly associated with the alternator such that the diesel engine drives the alternator. The alternator powers the main traction inverter, in which semiconductor power switches commutate the alternator output current to provide electrical power to electric drive motors of the wheel drive assemblies.
In both locomotive and OHV applications, solid state power converters are used to provide high voltage current from the generators or alternators to the wheel motors. Such power converters include inductive coils to step down the voltage as well as semiconductor power switches to commutate the current. Although the above-described applications are typical, it will be appreciated that power converters can be used in other settings.
Generally, operation of a power converter is accomplished by alternately applying two different gate drive voltage levels to the gates of individual semiconductor power switches via corresponding gate drive units. The gate of each power switch is a low power terminal used to turn the switch on or off by changing the concentrations of charge carriers within the semiconductor regions. Charge carrier concentrations may be changed by depletion, or by electric field, i.e., through field-effect and depletion-effect switching. Field-effect and depletion-effect semiconductor power switches respond differently, however, to any constant value of gate drive voltage, depending on electrical parameters of the circuit in which the semiconductors are connected. As such, power converter efficiency varies across the operating ranges of electrical parameters that impact semiconductor power switch response.
Accordingly, it is desirable to maintain optimum power converter efficiency by regulating witching current slew rates.